The vast majority of those fighting against the Assad regime are ordinary Syrians and defected soldiers fed up with the authoritarian government, analysts say, but increasingly foreign fighters and those adhering to an extremist Islamist ideology are turning up on the front lines. (ASSOCIATED PRESS, File)

PARIS (AP) — European governments have been among the most vocal supporters of Syria's rebels — to a point: Last week, Muslims in Britain and France accused of trying to join the fight against the regime were detained.

For security officials, the fear is that extremists with European passports who are alienated and newly trained to wage war will ultimately take skills learned in Syria and use them back home. In France, where an Islamic extremist trained in Pakistan attacked a Jewish school and a group of soldiers earlier this year, the fear is particularly acute.

French officials have jailed eight people, including one over the weekend, describing the group as a network of French-born radical Islamists bent on targeting Jewish groups at home and fighting holy war abroad. They said the cell attacked a kosher grocery with a grenade and had a structure in place to send Muslims to fight in Syria alongside the rebels.

"The enemies within will require vigilance and great determination," France's top security official, Interior Minister Manuel Valls, said Friday. "We know that there could be some who were not apprehended, who perhaps went abroad to fight."

Security officials worldwide have watched the aftermath of the Arab Spring with caution, particularly concerned that citizens who join the fight could return home more radicalized and with a new ability to carry out guerilla warfare. European officials have a particular concern: It's a short flight from the Mideast and the borders within the European Union are open for anyone with an EU passport or national ID, making undetected travel a simple matter.

"We have been keeping a close eye on who is going to Syria, but unlike Libya, there are multiple ways into the country and it's not as easy to track," said a European security official who spoke on condition of anonymity because she was not authorized to speak to the media. "Still, we're particularly concerned that people returning will come back with new skills that could present a threat to our security."

It's a sensitive and complex issue, say European intelligence officials. There's evidence that foreigners are joining the fight against Syrian President Bashar Assad, but their numbers — especially those from Europe — are believed to be small. But what is a minor issue in Syria could become a big issue in Europe, where many Muslims, even the native born, feel increasingly marginalized.

Syrian rebels are downplaying the newcomers' impact on the struggle to dislodge Assad. George Sabra, spokesman for the Syrian National Council, insisted last week that the foreign fighters presented no long-term problem for Syria: "They say they've come to help the Syrian people and they'll return home again."

That's precisely what many security officials are afraid of. Noman Benotman, a former jihadist fighter who now works for the London-based Quillium Foundation, offers an even more sobering view. He said it's not the warfare skills that security officials should fear but rather the sense of anger and lack of fear.

"There is an impression amongst some fighters in Syria that the West has abandoned them," said Benotman, who now works as an analyst for the anti-radicalization think tank. "After you're engaged in such a battle, you lose all sense of fear. This is exactly what al-Qaida recruiters look to as their dream opportunity for recruits."

He said fighters who return to Europe and elsewhere will have come back prepared for war — but without any obvious outlet.

"The radicalization process has already started" in Syria, he said. "If al-Qaida elements don't capitalize on this in Syria, they will do it anywhere they can. We've seen this before with Chechnya and other places."

Before Syria, it was the Iraq war which drew foreign radicals, including five Frenchmen of North African origin who were convicted of running a network to funnel French Muslims to fight against American forces.

The foreign mujahedeen who fought against the Soviet invasion of Afghanistan are the classic example. Osama bin Laden is the most notorious among them, but others include the first leader of the Islamist Abu Sayyaf separatist movement in the Philippines, and some of the first recruits for Jemaah Islamiyah, the terror group that ultimately carried out the Bali bombings in 2002, killing 202 people.

Britain is home to a large Muslim population and suffered a devastating 2005 terrorist attack perpetrated by British-born Islamists. Fears there that British Muslims might be slipping into Syria to join al-Qaida extremists were heightened in August when freelance photographer John Cantlie claimed he had been held hostage in July by a group of extremists including a man he identified as having a London accent.

On Tuesday, British police charged Shajul Islam, 26, in the kidnapping of Cantlie and fellow photographer Jeroen Oerlemans, and said Islam will appear in court on Wednesday. He was arrested Oct. 9 at London's Heathrow Airport. A 26-year-old woman who had been detained with him was released without charge Tuesday.

France, Syria's one-time colonial ruler and a strong supporter of the rebellion, was the first to recognize the opposition Syrian National Council, whose leaders again returned to Paris last week looking for backing. The administration has given millions in aid and non-lethal supplies, but President Francois Hollande has drawn the line at weapons, saying in a televised interview last week "when you supply arms, you never know where they're going to end up."

The same might be said of fighters: The French government is on the verge of passing a law that would bar citizens from training for terrorism abroad. The law stemmed from the March attacks in Toulouse by a radical Islamist born in France who received paramilitary training in Pakistan. The attacker, Mohammed Merah, killed seven people before dying in a shootout with police.

Valls, the French interior minister, has spoken out strongly, especially last week in the aftermath of the French arrests: "The terrorist menace is mutating."